If the discovery of a few presumed worm burrows is all it takes to unseat
the Cambrian explosion, it must not have been much of an explosion after
all! Having worked for years in the Cambrian, I have seen thousands of
feet of 'burrowed' sediments that to this day have no burrowers, and most
sedimentologists have no good explanation for their existence. They have
been called everything from burrows of unknown organisms to fucoids
(presumed casts of fucus...kelp), to purely sedimentary features. At this
time, nobody I have talked to has a clue. So I wouldn't be too quick to
throw out the Cambrian Explosion, which is worldwide in extent and
universal in scope [with the possible exception of Bryozoa and perhaps
Aschelmenthes(which have a miserable fossil record anyway), all of the
major phyla of animals appear in the Cambrian] on the basis of the report
in the popular press (or even in peer reviewed journals) of
sedimentological features that look like burrows. In fact given the amount
of effor that has been invested in teh Upper Precambrian lately, I would
say quite the opposite is true. The longer we look, the more we are going
to have to lean on worm tubes to support our suppositions that life existed
before the uppermost Precambrian. Might I suggest another good read for
those concerned about the early history of life and its origin (perhaps
with more success than my last suggestion) is a book by Wallace Arthur
(Cambridge Press, 1997) 'The Origin of Animal Body Plans: a study in
evolutionary developmental biology'.
Art
http://biology.swau.edu